Method and circuit for driving liquid crystal display, and portable electronic device

Abstract

A method for driving a liquid crystal display capable of reducing power consumption, decreasing a packaging area or a number of packaged parts, and providing an image of high quality when the liquid crystal display having a comparatively small display screen is driven by a line inverting driving method or by a frame inverting driving method.Digital video data is output, with or without data being inverted, based on a polarity signal being inverted in every one horizontal sync period or in every one vertical sync period. A plurality of gray scale voltages is selected, being provided so as to have either of a voltage of positive or negative to match an applied voltage of positive polarity or negative polarity transmittance characteristic. Any one of the gray scale voltage out of the plurality of gray scale voltages having a selected polarity is selected based on digital video data, with or without inversion of a polarity of gray scale voltages. The selected one gray scale voltage is applied as a data signal to a corresponding data electrode.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a method and a driving circuit for driving a liquid crystal display (LCD), and portable electronic devices employing the driving circuit and more particularly to the method and the driving circuit for driving the LCD used as a display section having a comparatively small display screen of portable electronic devices such as a notebook computer, palm-size computer, pocket computer, personal digital assistance (PDA), portable cellular phone, personal handy-phone system (PHS) or a like and to the portable electronic devices equipped with such the driving circuit for the LCD.[0003]The present application claims priority of Japanese Patent Application No.2001-008322 filed on Jan. 16,2000, which is hereby incorporated by reference.[0004]2. Description of the Related Art[0005]FIG. 20 is a schematic block diagram for showing configurations of a driving circuit for a conventional color LCD 1. The...

AI Technical Summary

Benefits of technology

[0027]In view of the above, it is an object of the present invention to provide a method and a driving circuit for driving an LCD, being capable of reducing power consumption, decreasing a packaging area or a number of packaged parts and providing an image of high quality when the LCD having a comparatively small display screen is driven by a line inverting driving method or by a frame inverting driving method and portable electronic devices employing the above driving circuit.

[0033]Also, a preferable mode is one that wherein includes a step of determining whether the digital video data is output, with or without the digital video data being inverted, based on a combination of a logic between a data inverting signal and the polarity signal, instead of inverting the digital video data, in order to reduce power consumption.

[0049]With the above configurations, the driving circuit is constructed so that digital video data is output, with or without the digital video data being inverted, based on a polarity signal which is inverted in every one horizontal sync period or in every one vertical sync period, that a plurality of gray scale voltages is selected which is provided so as to have either of a voltage of positive or negative out of a plurality of gray scale voltages of positive and negative polarity set in advance to match an applied voltage of positive or negative polarity—transmittance characteristic in the LCD, that any one of the gray scale voltage out of a plurality of gray scale voltages having a selected polarity is selected based on digital video data, with or without a polarity of the gray scale voltage being inverted, and that the selected one gray scale voltage is applied as a data signal to corresponding data electrode. Therefore, even when an LCD being used as a display screen whose area is comparatively small is driven by a line invert driving method or by a frame invert driving method, power consumption can be reduced.

[0051]With still another configuration, the gray scale voltage selecting circuit has a plurality of P-channel MOS transistors to which a plurality of gray scale voltages on a high voltage side, out of a plurality of gray scale voltages including a supply voltage to a ground voltage, is applied and a plurality of N-channel MOS transistors to which a plurality of gray scale voltages on a low voltage side is applied and is adapted to turn ON any one of the N-channel MOS transistors and the P-channel MOS transistors based on digital video data and outputs a corresponding voltage. Therefore, unlike the conventional case, use of a transfer gate is not required to construct the gray scale voltage. As a result, the number of component elements can be reduced to a half. Therefore, packaging area on a printed board can be reduced. An IC circuit such as a Chip on Glass (COG) making up the data electrode driving circuit can be made small in size, that is, a chip size can be made smaller. This enables it to make small and lightweight portable electronic devices which are driven by the battery, such as the notebook computer, palm-size computer, pocket computer, PDAs, portable cellular phone, PHS or a like. Also, since the number of the MOS transistors required to construct the gray scale voltage selecting circuit can be reduced to a half of those used in the conventional case, their parasitic capacitance can be reduced to a half which enables power consumption in the gray scale voltage generating circuit and the gray scale voltage selecting circuit to be reduced to about a half. This makes it possible to reduce power consumption in portable electronic devices described above and possible to make use time longer. Moreover, since amounts of charging and discharging currents flowing through the gray scale voltage generating circuit and time during which the charging and discharging currents flow can be reduced, unlike in the conventional case, no inferior contrast in the screen of the color LCD occurs. Furthermore, since the applied voltage—transmittance characteristic differs depending on whether the applied voltage is of positive polarity or of negative polarity, the driving circuit is so configured that the gray scale voltage of positive polarity and negative polarity, which makes it easy to make color correction and possible to obtain image of high quality.

Problems solved by technology

Furthermore, it is inevitably necessary to make small and lightweight the portable electronic devices being driven by the battery or the like such as the notebook computer, palm-size computer, pocket computer, PDA, portable cellular phone, PHS, or the like.

This produces a bottleneck in scaling down and making lightweight the portable electronic devices.

This produces a bottleneck in reducing power consumption in the above portable electronic devices.

Therefore, when the gray scale voltages VI1 to VI9 each having the same voltage but the opposite polarity are used, there is a problem in that color correction is difficult and an image of high quality cannot be obtained.

Moreover, the above inconveniences occur even in a driving circuit of a monochrome LCD in the same manner as described above.

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